SILVERING COPPER PLATES.

Tuapeka Times, Volume XVIII, Issue 1173, 22 August 1885, Page 3

SILVERING COPPER PLATES.

When Professor Black was in Lawrence recently, in the presence of some miners and others, he showed how copper-plates for the battery-tables could be coated with mercury in such a manner that there was little fear of their becoming covered with verdigris. He explained that the usual practice was to clean the copperplate- with nitric acid, and then to coat it with quicksilver. This was an easy and quick way, but had the great fault that before the plate was in use long green patches soon began to show through the silvered surface. This was invariably the case when the acid was used to clean the plate. With the process, which he would show them no acid was used ; a better surface was secured, and the result was more permanent. The process was simple enough, and anyone once seeing it done' could always do it again. Clean the plate as thoroughly as possible by scouring it with sand, atid then wash the surface with a strong solution of caustic soda or potash. This was the very reverse of an acid, and destroyed every trace of acid that might accidentally be upon the plate. ' Then rub in the< quicksilver, treated previously with sodium amalgam. This was' done in presence pf several onlookers, and in a short' time the piece of copper-plate was beautifully and regularly coated with mercury. Professor Black made some sodium amalgam, and fully explained tho process. A small quantity of quicksilver was slightly warmed, until it was just hot enough to place the finger in without getting it burned ; some pieces of metallic sodium were then thrown into the mercury and pressed beneath it with a splinter of wood. Instant combination took place, with a flash of flame and a puff of smoke. The operation was repeated until sufficient sodium had combined with the mercury to form the amalgam. The books stated that the operation was very dangerous. That was because they wanted chemists to have a monopoly in the manufacture of sodium amalgam. Those present could see for themselves that there was no danger. All that was necessary was to heat a little mercury in a teacup over boiling water, and then to plunge Blices of sodium into the heated liquid. When sufficient sodium had been added and well stirred into the mercury, it could be ; poured out upon a shovel or some other clean place where it would solidify. Sodium amalgam, as well as sodium itself, had to be kept in kerosene or rock oil. Then when the mercury in use on the amalgamating tables began to "sicken," a little of the amalgam stirred into it quickly cleared it up to its original brightness. Before coating a copper-plate with quicksilver, a little of the amalgam was added, which made the operation easy and certain. Plates so coated would keep bright for a long time, and if a green spot did appear a rub with sand and a touch up with the solution of caustic soda and mercury soon rectified it. Every mine manager could easily enough make his own sodium amalgam, and that far cheaper than the imported article could be bought. Sodium would cost about 20s per lb in New Zealand, and one pound of it was sufficient to do 251bs of mercury. Sodium amalgam could be made by the miner himself for about the same price per lb which it cost per ounce when imported.